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Surgeons should use caution when injecting, aspirating after joint replacement

Mark J. Spangehl, MD, believes aspiration is best for a total joint replacement when trying to exclude or diagnose infection.

Issue: July 2006

ByDouglas W. Jackson, MD

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Admitting that that one of your patients has an infected joint replacement is very difficult for any surgeon. When a postoperative arthroplasty patient experiences persistent pain and/or swelling, deep infection is part of the differential diagnosis workup. Needle aspiration is a cost-effective assessment that may be diagnostic.

For this month’s interview, I asked Dr. Mark J. Spangehl at the Mayo Clinic Arizona in Scottsdale how he uses joint aspiration in a patient who has persistent postoperative symptoms following a joint replacement. He offers a practical approach to this potentially perplexing clinical situation.

Douglas W. Jackson, MD: When do you recommend aspiration of a total joint replacement?

Mark J. Spangehl, MD: Aspiration of a total joint replacement is used as part of the work-up of a painful arthroplasty. It is recommended when trying to exclude or diagnose infection and also in the less common situation when a surgeon is suspicious of a crystalline arthropathy (gout or pseudogout). If there is any history of infection during the clinical evaluation (ie, wound healing problems, prolonged drainage, history of prolonged postop antibiotic use), or if the inflammatory markers — erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) — are elevated, then we obtain an aspiration.

When assessing the inflammatory markers, both the ESR and CRP must be normal. Most literature uses a cutoff of 30 or 35 mm/hr for the ESR and <10.0 mg/l for the CRP as acceptable values when excluding infection.

The surgeon also needs to interpret both these values together when deciding upon an aspiration. For example, if both are high-normal, such as an ESR of 28 and a CRP of 9.2, then I would aspirate the joint, suspecting a low virulent infection. But if either one is very low-normal (eg, ESR 5 or CRP 1.8) and the other value is also in the normal range, aspiration isn’t necessary to rule out infection.

Crystalline arthropathy can occasionally present as an acutely painful total joint replacement and should be considered part of the differential diagnosis when one suspects an acute hematogenous infection. An acute crystalline arthropathy can result in elevated inflammatory markers. Therefore, in these situations, the aspirate should also be sent for crystals.

Jackson: If it is infected, how often can one obtain a positive culture and sensitivity with an aspiration in the office?

Spangehl: Aspiration in the office needs to be performed under the strictest aseptic technique, both to reduce the chance of false positive contamination, and to prevent the rare but real chance of contaminating a sterile arthroplasty.

Aspirations done in the office would most commonly be the knee, as hip aspirations need to be done under fluoroscopic guidance. Shoulders and elbows could be aspirated in the office as well.

For knees, the literature does not differentiate between aspirations done in the office vs. some other setting such as a hospital or radiology suite; therefore, with proper technique, I think the yield for obtaining positive cultures in infected cases should be good. One needs to ensure that the patient has been off all antibiotics for a minimum of 2 weeks, preferably 3 or 4 weeks, to reduce the risk of false negative cultures. Their medication list needs to be reviewed, and patients specifically asked if they are on antibiotics or if any new medications have been recently started, as it is at times surprising that patients are on antibiotics without direct knowledge.

Once the knee is aspirated, a fresh needle is used to inject the aspirate into the culture bottle. We generally send two specimens to help with the interpretation of results, namely both negative is more likely to indicate a true negative and conversely both positive more likely to be a true positive.

Jackson: When aspirating a joint to rule out infection, what do you usually order when sending the specimen?

Spangehl: The aspiration is routinely sent for aerobic and anaerobic cultures. In patients who have been previously investigated or managed for presumed infection with negative cultures, or in patients who are immunosuppressed (eg, transplant patients, HIV positive, cancer patients undergoing chemotherapy) the specimen is also sent for fungal and mycobacterial cultures.

If sufficient fluid is present, which is usually the case, the aspirate is also sent for synovial white cell count and differential. A synovial white cell count of greater than 2000 cells/ml or greater than 65% polymorphonuclear leukocytes is strongly suggestive of infection.

As noted above, in cases of acute pain with suspected acute hematogenous infection, in addition in culture, Gram stain and synovial cell count, analysis for crystals is also requested.

Jackson: What are your feelings about using intra-articular injections as diagnostic for unexplained postoperative joint pain?

Spangehl: Intra-articular diagnostic blocks are very helpful in the workup of pain around a total joint. We frequently use blocks to help sort out a patient’s pain pattern when the clinical presentation is not obvious for a diagnosis.

Some examples are: 1) the presentation of atypical hip pain (pain localized only to the buttock area, or only the distal thigh and knee), particularly in someone who also has a finding, either radiographic or clinical, of degenerative disc disease or knee pathology; 2) when you are suspicious that the pain is arising from the joint replacement, but initial radiographs don’t show an obvious diagnosis in that joint; 3) or lastly, when you are reasonably certain of the correct diagnosis, but the patient may have more than one diagnosis resulting in pain around the joint and you or the patient needs some reassurance that, in fact, the majority of symptoms are arising from the joint in question.

As with joint aspiration, strict aseptic technique must be used. The site needs to be thoroughly prepped, and a simple alcohol wipe is probably not sufficient. Previously opened bottles of local anesthetic should not be used, and a separate needle for aspiration from the bottle and for the injection is also worthwhile.

Jackson: Do you ever consider a cortisone injection in a patient with persistent effusion following joint replacement?

Spangehl: If you are injecting something into a total joint replacement, you need a really good reason to do it. Aspirating to diagnose or exclude infection or to perform a local anesthetic block are good indications and generally yield useful information. However, injection of cortisone is less likely to be useful and may potentially be harmful.

It is unlikely that an intra-articular cortisone injection will resolve the problem that is causing the effusion. Therefore, you need to ask yourself: What is being accomplished with the injection of cortisone?

I have not performed cortisone injections into total joints and would generally not support their use in this situation. If a patient presents with a persistent effusion, you need to do a thorough evaluation to exclude other diagnoses.

I know of one case in which a patient with persistent knee effusions — whose initial aspirations were negative for infection — was given repeated cortisone injections and ultimately presented with a coagulase-negative Staphylococcus infection.

Unless there is a compelling reason to do it, I would be very cautious of this practice and avoid intra-articular cortisone injections into total joints.

For more information:

• Mason JB, Fehring TK, Odum SM, Griffin WL, Nussman DS. The value of white blood cell counts before revision total knee arthroplasty. J Arthroplasty. 2003;18:1038-1043.
• Spangehl MJ, Masri BA, O’Connell JX, Duncan CP. Prospective analysis of preoperative and intraoperative investigations for the diagnosis of infection at the sites of 202 revision total hip arthroplasties. J Bone Joint Surg. 1999;81A:672-683.
• Trampuz A, Hanssen AD, Osman DR, et al. Synovial fluid leukocyte count and differential for the diagnosis of prosthetic knee infection. Am J Medicine. 2004;117:556-562.